Various heat transfer recording methods have been known so far. Among these methods, dye diffusion transfer recording systems attract attention as a process that can produce a color hard copy having an image quality closest to that of silver halide photography. Moreover, this system has advantages over silver halide photography which is a system with treatment chemicals, and it enables direct visualization from digital data, it makes reproduction simple, and the like.
In this dye diffusion transfer recording system, a heat-sensitive transfer sheet (hereinafter also referred to as an ink sheet) containing dyes is superposed on a heat-sensitive transfer image-receiving sheet (hereinafter also referred to as an image-receiving sheet), and then the ink sheet is heated by a thermal head whose exothermic action is controlled by electric signals, in order to transfer the dyes contained in the ink sheet to the image-receiving sheet, thereby recording an image information. Three colors: cyan, magenta, and yellow, are used for recording a color image by overlapping one color to other, thereby enabling transferring and recording a color image having continuous gradation for color densities.
Recently, printers in thermal transfer recording process are becoming more popular, because of their convenience in handling and high-quality image. These printers are used under various temperature and humidity environments.
For reduction in environmental load, heat-sensitive transfer image-receiving sheets produced by aqueous coating, for example those containing a latex polymer in a receptor layer, were proposed (see JP-A-2006-88691 (“JP-A” means unexamined published Japanese patent application), JP-A-2006-82382 and JP-A-2007-190909), but these heat-sensitive transfer image-receiving sheets caused additional problems, for example, of browning in the high-density region of near-black image and deterioration in glossiness after printing under high-humidity environment.
Presence of water at the interface between the heat-sensitive transfer sheet and the heat-sensitive transfer image-receiving sheet during printing often exerts such an influence, and the influence is particularly distinctive in these heat-sensitive transfer image-receiving sheets prepared by aqueous coating.
Therefore, there exists a strong need for means to overcome the problems.